The goals of project 3 are to develop novel therapeutic approaches for the treatment of localized malignancy, such as mesothelioma, and to obtain important information about the biology of adenovirus-mediated gene transfer in cancer therapy. Malignant mesothelioma, a tumor arising from the lining of the pleural or peritoneal mesothelial cells, is characterized by aggressive local, rather than distant, spread for its attendant morbidity and mortality and mortality and is extremely resistant to treatment despite aggressive multimodality therapy. Studies by others using packaging cells secreting a retrovirus containing the Herpes Simplex thymidine kinase (HSVtk) gene followed by treatment of animals with the anti-viral drug ganciclovir (GCV) have demonstrated brain tumor regression. Recently completed studies show that injection of an adenovirus vector containing the HSVtk gene (Ad.RSVtk) followed by treatment with GCV can eradicate established human mesothelioma tumors growing with the peritoneal cavity of immunodeficient mice. These results suggest that administration of HSVtk/GCV using adenovirus may be efficacious in patients with this disease, as well as in other forms of cancer where localized spread is detrimental (i.e. brain tumor, ovarian cancer, leptomeningeal-metastasis, bladder carcinoma). Malignant mesothelioma thus represents an ideal "model" tumor system in which to test this hypothesis and to obtain valuable information about the biology of adenovirus-based gene therapy for localized malignancy in humans. After toxicity studies have been completed in animals, a Phase i clinical trial will begin in which patients with mesothelioma will be given intrapleural administration of Ad.RSVtk followed by treatment with GCV for 14 days. This study will define the potential systemic, intrathoracic, and immunologic toxicities and determine the maximal tolerated dose. An important feature of this protocol includes a videothoracoscopic biopsy of tumor three days after virus instillation that will allow the amount of gene transduction within the cells of the tumor and the type of immune response generated to be determined histologically. It is hypothesized that specific histologic featrues (including degree of fibrosis and vascularity, degree of expression of vitronectin receptor, and degree of immune response generated) will correlate with the efficiency and efficacy of the Ad.RSVtk/GCV system in mesothelioma patients with less extensive "non-bulky" disease. Using this information, the safety and efficacy of new viral vectors developed in Projects 1 and 2 will be tested in additional Phase I and Phase II clinical trials.